The subject of this invention is a method to inhibit paint-product skin formation on the interior surface of the lid of a closed upright vessel housing a paint composition wherein a portion of said composition is volatile.
Paint compositions generally contain a volatile portion which volatilizes into the atmosphere upon application of the paint composition to a substrate, thereby essentially coating the substrate with the paint composition minus its volatile portion. In latex paint compositions, for example, water is the volatile portion which volatilizes from the composition after application of the paint composition to the substrate. Providing such a paint composition to an ultimate user is generally accomplished by supplying the composition in a closed upright vessel, usually a metal can, having a top lid which is removable to permit access to said vessel. However,when the composition is initially delivered to the vessel, said vessel may not be completely filled in order to allow a later addition of pigment formulations to accommodate ultimate color needs. Further, even when later additions are not contemplated and the vessel is initially completely filled, a settling effect occurs over time to yield a vessel which, likewise, is not completely filled. In either case, therefore, an air space results between the top of the paint composition and the interior surface of the vessel lid.
Normal handling of this vessel during shipment and storage of the paint composition therein can easily initiate the formation of a paint-product skin on the interior surface of the vessel lid. The term "paint-product skin" is herein defined as a coating of the paint composition minus at least a part of the quantity of the originally-present volatile portion of said paint composition. Specifically, tipping or inverting the closed upright vessel from its upright position causes the paint composition in the vessel to contact the interior surface of the lid. Returning the vessel to its upright position results in a coating of the paint composition being retained on this interior surface. The combination of this coating, which is similar in thickness to a normally applied coating in a painting process, on the interior surface of the lid along with the air space discussed above acts to cause a paint-product skin to form on the interior surface of the lid since at least a part of the volatile portion of the paint composition volatilizes into the air space. In particular, if the paint composition is a latex base containing water, this water tends to volatilize from the coating on the interior surface of the lid and into the air space. When water migrates in this manner from the coating, a paint-product skin forms on the interior surface, said skin ranging from a hard, dry film to a soft gelatinous layer. This paint-product skin can later break loose and fall into the paint composition, causing lumps, grit and the like in the composition which will cause surface irregularities and constitute a form of seeding when the composition is applied to a substrate to be coated.
It is therefore an object of the instant invention to inhibit paint-product skin formation on the interior surface of the lid of a closed upright vessel housing a paint composition wherein a portion of said composition is volatile, thereby eliminating seeding and consequent irregularities upon application of the composition to a substrate. It is a further object of the invention to conveniently inhibit said skin formation from a paint composition wherein the volatile portion of the composition is water as in a latex paint composition. These and other objects will become apparent within the body of this application.